The present invention relates to a rear suspension system for a vehicle, and more particularly to a dual link strut type rear suspension system.
JP-UM 58-188308 discloses a rear suspension system for a vehicle. This known rear suspension system comprises an axle carrier rotatably carrying a rear road wheel, a front lateral link, a rear lateral link, a radius rod and a strut. The front and rear lateral links have inboard ends, each pivotably mounted via an elastic bush to the vehicle body. Outboard end of the front lateral link is pivotably mounted via an elastic bush on the axle carrier at a front pivot portion, while outboard end of the rear lateral link is pivotably mounted via an elastic bush on the axle carrier at a rear pivot portion. The radius rod has a front end pivotably mounted via an elastic bush on the vehicle body and a rear end pivotably mounted via an elastic bush on the axle carrier at a third pivot portion. The arrangement is such that the front and rear lateral links are of the same length and the front pivot portion is disposed outboard of the rear pivot portion. With this arrangement, a toe angle of the rear road wheel is varied toward a toe-in side when the vehicle bumps along the road. When the vehicle bumps along the road, the road wheel is displaced upward. Since the front and rear lateral links are of the same length and the front pivot portion is disposed outboard of the rear pivot portion, the front pivot portion is upwardly displaced about the inboard bush of the front lateral link further than the rear pivot portion is displaced about the inboard bush of the rear lateral link, thereby varying the toe angle of the road wheel toward a toe-in side. The front lateral link extends over the radius rod and thus the front pivot portion is disposed at a level higher than the rear pivot portion to provide a clearance between the front lateral link and the radius rod.
With this known rear suspension system, the toe angle of the road wheel is varied toward a toe-out side when the road wheel is subject to a transverse force directed inboard of the vehicle, since the front pivot portion is disposed outboard of the rear pivot portion. On the contrary, when the road wheel is subject to a transverse force directed outboard of the vehicle, the toe angle of the road wheel is varied toward a toe-in side. This compliance steer due to transverse force causes a steering characterstic of the vehicle to shift toward an oversteer side since a toe angle of the outer rear wheel is varied toward a toe-out side, while a toe angle of the inner rear wheel is varied toward a toe-in side when the vehicle is making a turn. This reduces stability of the vehicle upon making a turn.
Another problem is that restriction is imposed on vertical layout of a radius rod, since the radius rod extends under a front lateral link.
JP 59-130712 A discloses a rear suspension system which has solved the first one of the above-mentioned problems. This known rear suspension system comprises an axle carrier rotatably carrying a rear road wheel, a front lateral link and a rear lateral link, a radius rod and a strut. Inboard ends of the front and rear lateral links are pivotably mounted via an elastic bush on the vehicle body, while outboard ends of them are pivotably mounted via an elastic bush on the axle carrier at a front pivot portion and a rear pivot portion, respectively. A rear end of the radius rod is pivotably mounted via an elastic bush on the axle carrier at a third pivot portion and a front end thereof pivotably mounted on the vehicle body. The strut extends vertically from the axle carrier and has an upper end mounted via an insulator on the vehicle body. As viewed in the vehicle longitudinal direction, the front lateral link is disposed at a level lower than the rear lateral link is. When a transverse force directed inboard of the vehicle is applied to a lower end portion of the rear road wheel, different reaction forces are induced at the front pivot portion and the rear pivot portion. The reaction force induced at the front pivot portion becomes greater than the reaction force induced at the rear pivot portion, since the axle carrier is considered to pivot toward the inboard of the vehicle about the mounting insulator via which the strut is mounted on the vehicle body. Under this condition, the inboard and outboard elastic bushes of the front lateral link are compressed more than the elastic bushes of the rear lateral link are. This results in varying a toe angle of the outer rear wheel toward a toe-in side and a toe angle of the inner rear road wheel toward a toe-out side when the vehicle makes a turn. In this known rear suspension system, the front lateral link extends under the radius rod.
According to this known rear suspension system, the increased rigidity of the front lateral link is required to withstand a greater transverse input force, causing an increase in weight and manufacturing cost. Another problem encountered with this known rear suspension system is that the radius rod can not be inclined vertically because there is no clearance between the front lateral link and the radius rod.
Usually, inboard ends of front and rear lateral links are pivotably mounted via an elastic bush on a suspension member and a front end of a radius rod is pivotably mounted via an elastic bush on the suspension member as clearly shown in FIG. 3 of JP 60-116513 A. According to this known construction, the suspension member has a front mount portion mounted via an insulator on the vehicle body and a rear mount portion mounted via an insulator on the vehicle body. The front mount portion is disposed forward of where the front end of the radius rod is mounted on and the rear mount portion is disposed rearward of the lateral link. This arrangement makes it difficult to provide a space, between the suspension member and a spare tire pan, which a fuel filler hose can extend through.